You may be wondering why it matters whether your sentence is the fragment kind of messed-up or the run-on kind of messed up. Well, it matters because you have to do different things to fix different types of sentence errors. A person with the flu needs different medical attention than a person with a fragmented femur (see what I did there?). First let’s diagnose the type of malady that’s plaguing your sentences, then we’ll write a prescription for fixing them.
If you have a fragment, then you’ve put a period after an incomplete thought. A fragment may be a phrase that doesn’t have a subject and a verb. Here’s an example: “Running quickly toward the water fountain.” Or, it may be a clause that does have a subject and a verb but doesn’t express a complete thought. Here’s another example: “Because she was so strong.”
If you have a fragment, the solution is to add the information necessary to complete the thought logically. If you’re missing a subject or a verb, figure out what it is and add it. If you only have a dependent clause, make sure that you add an independent clause that will complete the thought. Let’s fix the previous examples. We could say, “Running quickly toward the water fountain, Morgan was parched.” Fixing the second fragment would look like the following: “Because she was so strong, she was able to help push the Toyota toward the gas station.”
Run-ons have the opposite problem of fragments. Instead of not having a complete thought, they have multiple thoughts incorrectly joined. Here’s an example: “I like running I specifically like running in 5K color runs.” Why is this a run-on? It’s because we have two sentences running into each other: “I like running” and “I specifically like running in 5K color runs.” Here’s another example: “She works at the theatre on Tuesdays on Wednesdays she works at Family Flix.”
If you have a run-on, you need to focus on adding the correct punctuation or completely separating ideas into multiple sentences. We can apply this to the above examples. The first run-on could be fixed by adding a comma and a conjunction: “I like running, but I specifically like running in 5K color runs.” We could fix the second sentence in the same way, or we could simply make the two thoughts into separate sentences: “She works at the theatre on Tuesdays. On Wednesdays, she works at Family Flix.”